1. Field of the Invention
The present invention relates to a single crystal silicon carbide substrate and a method of manufacturing the same.
2. Description of the Background Art
A single crystal silicon carbide substrate has been employed in recent years as a substrate for use in manufacture of a semiconductor device. In particular, a single crystal silicon carbide substrate having a 4H polytype as a crystal structure is especially useful due to its high electron mobility. In order to obtain such substrate, methods of manufacturing an ingot made of single crystal silicon carbide having the 4H polytype have been under consideration.
According to a method disclosed in Japanese Patent Laying-Open No. 09-157091, for example, a source material made of silicon carbide is sublimated by heating, and supplied onto a seed crystal made of single crystal silicon carbide, to grow single crystal silicon carbide on this seed crystal. During this process, an impurity (nitrogen) is introduced with a concentration of 5×1018 cm−3 or more into carbon atom sites. According to this publication, the introduction of the impurity to substitute for the carbon atom sites allows a high-quality 4H-type single crystal silicon carbide to grow with high reproducibility.
During growth of a single crystal on a seed crystal, both spiral growth and step-flow growth take place. In the single crystal thus obtained, a facet region formed by the spiral growth and a non-facet region formed by the step-flow growth coexist. Accordingly, even if the facet region and the non-facet region are both of high quality, there is a significant difference in physical properties between them, resulting in wide variation in physical properties of the single crystal. As a result, in-plane variation in physical properties of a substrate cut from this single crystal increases as well. Specifically, nitrogen atom concentration tends to be high in the facet region and tends to be low in the non-facet region. Thus, in-plane variation in nitrogen atom concentration in the substrate increases.